<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Test01</title>
</head>
<body>
<script type="text/javascript">
    class MyDate extends Date {
        constructor() {
            super();
        }

        test() {
            console.log(this.toISOString());
        }
    }

    let date01 = new MyDate();

    console.log(date01.getFullYear());

    date01.test();
    
</script>
</body>
</html>